Looking for an exotic retirement destination? Here’s a new possibility for you: Mars.

No, we’re not kidding.

Billionaire Dennis Tito, the engineer-turned-investment-mogul who in 2001 became the first-ever space tourist by buying a seat on a Russian space mission, wants to find a mature man and woman to serve as as a two-person crew on a private interplanetary fly-by. According to his Inspiration Mars Foundation, Tito hopes to launch in 2017 so as to be able to take advantage of a planetary alignment that occurs only once every 15 years and that would allow astronauts to travel to Mars and back in only 501 days.

Tito’s chief technologist, Taber MacCallum, recently told Yahoo News that the ideal candidates for the mission would be a married couple 50 or older. He says that their years of getting along together and the good judgment developed over several decades of adulthood would prove useful on a long space mission. That’s the flattering part. Pragmatically, because cancer often takes a long time to develop, he and the other planners of the mission are thinking that an older couple won’t face as much risk from being subjected to radiation for an extended period in space or in Mars’ orbit.

“We need to properly represent humanity, so that’s a man and a woman,” MacCallum said. “The crew also needs, for radiation reasons, to be older, in the mid-50s, and this better be a man and woman that have a lot of experience together, so preferably married. . . . It’s a really interesting message, though, in the end that it’s really cool to be an older couple.”

In intergalactic space, where there’s no atmosphere like the one on Earth to filter radiation, doses can be from 100 to 1,000 times higher than we’re accustomed to experiencing, according to Space.com. The Register, a British technology publication, reports that radiation measurements taken during the Mars rover Curiosity’s exploration of the Red Planet suggest that the average person’s risk of eventually developing a fatal cancer on Earth, which is around 20 to 25 percent, would increase around 3 percent. That’s one of the many reasons NASA has been proceeding slowly with Mars ambitions, and why researchers are working to develop radiation-shielding technology, such as the use of walls filled with hydrogen gas. The passive shielding used in the International Space Station, which is made of polyethylene plastic, would require layers 30 or more feet thick to provide adequate protection.

There is a precedent for older astronauts. Former Sen. John Glenn (D-Ohio), who orbited the Earth as a Mercury astronaut in 1962, revisited space again in 1998 at age 77 as a member of the crew of the Space Shuttle Discovery. He apparently experienced no ill effects from his nine-day mission.